Autocrine growth stimulation by transforming growth factor-α in human non-small cell lung cancer

We studied the biological response to and production of transforming growth factoralpha (TGF-α) by the non-small cell lung carcinoma (NSCLC) clonal cell lines H226b, H322a, H460a, H596b. Each of these cell lines expressed epidermal growth factor receptor (EGFR) as determined by [¹²⁵I]EGF competitive binding and Scatchard analysis and by phosphorylation. The receptors were functionally active as determined in immune complex kinase assays. H322a, H226b, H460a, and H596b cells showed stimulated [³H]thymidine (Thd) uptake in response to TGF-α. Exogenously added TGF-α increased colony formation in soft agar for three of the cell lines in media containing serum. All cell lines expressed TGF-α detected by immunohistochemistry and TGF-α mRNA, although to differing degrees. Cell lysates and spent media competed for EGFR binding with EGF, thus demonstrating production of TGF-α-like activity. The anti-TGF-α monoclonal antibody AB-3 inhibited the uptake of [³H]Thd by proliferating H322a and H226b cells but not H460a and H596b cells. No inhibition occurred with MOPC21 antibody and inhibition was completely reversed by addition of TGF-α to the culture. Suramin inhibited cell proliferation and [³H]Thd uptake by all cell lines. Inhibition of H460a and H596b cells was reversed with exogenous TGF-α but not PDGF. Our data suggests that TGF-α is a mediator of autocrine growth stimulation for NSCLC cells, and that for some NSCLC cells cytoplasmic binding of receptor and ligand is the primary mechanism for autocrine growth stimulation.